A drum refiner has an element which is attachable to the rotor shell and comprises crushing or grinding surfaces having increasing diameters. Crushing or grinding surfaces of steeper inclination in relation to the rotor axis which are immediately adjacent to other crushing or grinding surfaces of this type are subject to wear. This is especially true when the crushing or grinding surfaces are conical shaped. Such surfaces must be repeatedly replaced during the use of the drum refiners to assure appropriate crushing or grinding performance.
Most prior art refiners are used for the mechanical production of wood pulp. They comprise a disk equipped with grinding plates rotating about a horizontal axis. An opposing disk corresponding with this disk is also provided with grinding plates which can be either rotating or stationary. In these known embodiments, at least an essential portion of the grinding gap extends vertically or inclined towards the axis of rotation in the area of the marginal zone. Since high contact pressure of the grinding plates is required for the grinding operation, the aforementioned known embodiment causes excessive stress on the material and above all on the bearings which limits the maximum admissible refiner throughput. The resulting use of high mechanical energy causes the generation of considerable amounts of steam in the grinding gap because mainly wet or humid material is ground. For a good utilization or recovery of energy and a largely unhampered charging of the chips or the like, an adequate discharge of the steam together with the fibrous material thus produced or recovered is aimed at, but difficult to put into practice because of the large amount of steam generated. Particularly aggravating is the vertical arrangement of the grinding gap in conventional disk refiners, as these bring about a partial separation of the fibrous material and a strong backflow of the generated steam.
A refiner is known per se in which a conical trunnion is provided on its periphery with crushing bars of varying lengths and arranged in the conical interior space of a housing whose interior wall is provided with corresponding opposing bars so that a grinding gap of 1 to 2 mm dimension results. The material feed is effected on one side of the machine within the area of the trunnion shaft. The output of this refiner is unsatisfactory because the material feed is effected from only one side and immediately on the shaft directed into the conical grinding gap. There is no satisfactory defibration and no adequate pulping effect. This also applies in a similar manner to the known conical refiners.
Also belonging to the state of the art is a microatomizer in which grinding stock is fed centrally from the top via a screw conveyor to hollanders extending parallel to the axis of a separator impeller wheel, the hollanders forming a gap extending parallel to said axis with the housing receiving said impeller wheel which is provided with small notches on its inner wall. The grinding stock ground in the parallel gap is conveyed toward the center of the grinding zone by an air stream and in doing so passes said separator impeller wheel. The coarse grinding matter separated therein is returned to the grinding zone. Two blower wheels arranged on both sides of the grinder shaft generate the required air stream. Aside from the fact that in this known embodiment, there are no conical grinding gaps or the like adjacent the grinding gaps parallel to the axis, it is not suitable for processing chips or other wet fibrous material, not to mention its elaborate construction.